CN100422373C - A kind of high-strength low-alloy atmospheric corrosion-resistant steel and its production method - Google Patents

Abstract

The invention relates to a high-strength atmospheric corrosion-resistant steel and a production method thereof. It mainly solves the technical problems that the yield strength of the existing atmospheric corrosion-resistant steel does not reach the level of 550MPa and the low-temperature impact toughness is not good. A low-alloy atmospheric corrosion-resistant steel, the weight percentage of chemical composition is: C: 0.05-0.10%, Si≤0.75%, Mn: 1.0-1.6%, P≤0.020%, S≤0.010%, Al: 0.01-0.05% , Cu: 0.20-0.55%, Cr: 0.20-0.45%, Ni: 0.12-0.40%, Ca: 0.001-0.006%, N: 0.001-0.006%, in addition to Nb≤0.07%, Ti≤0.025%, Mo ≤0.35% of two or more, the balance is Fe and unavoidable impurity elements. The production method is to adopt the conventional smelting process. After the billet is reheated above 1200°C, it adopts two-stage controlled rolling, and the finish rolling starts above 950°C. The cumulative reduction rate is ≥80%, and the finishing rolling temperature is lower than 880°C. Cool at a cooling rate of 5-15°C/S to 400°C to 700°C for coiling, then air-cool to room temperature. Used in vehicles, containers, bridges, building structures, towers, columns, construction machinery, etc.

Description

A kind of high-strength low-alloy atmospheric corrosion-resistant steel and its production method

Technical field:

The invention relates to a high-strength atmospheric corrosion-resistant steel and a production method thereof, belonging to the field of low-alloy steel manufacturing.

Background technique:

Before the present invention, there have been many invention patents on atmospheric corrosion-resistant steel (weathering steel), the "Atmospheric Corrosion-Resistant Low-alloy Structural Steel (Patent No. steel (patent number: 85108118)", and "atmospheric corrosion-resistant steel (patent number: 00121262.1)" published in 2001. These patented steels are all low-alloy structural steels with certain atmospheric corrosion resistance, the composition system is Cu-P-Cr-Ni or Cr-P-Ti-RE, the yield strength is 350MPa, and the low-temperature impact performance is relatively high. Low.

The patent most similar to the patent of the present invention is the Chinese patent application "Acicular Structure High-Strength Weathering Steel and Its Production Method" published in 2005 (patent application number: 200410061112.4), see Table 1 "Comparative Patent 1" for details. The invention patent also belongs to the field of low alloy steel manufacturing. The composition design adopts extremely low carbon, the addition of Cu-Cr-Ni-Mo-Nb and the compound addition of two or more of Ti-Al-Zr-RE or Ca to control the carbon content at close to or below normal temperature The maximum solubility of carbon in α-Fe is 0.0218%, so as to reduce or inhibit the precipitation of cementite, and ensure that the main control structure is a uniform acicular structure, so as to obtain excellent weather resistance. This patent application adopts an extremely low carbon content design that is very difficult to smelt. The carbon content is 0.01-0.04%, which greatly increases the production difficulty and manufacturing cost, and its achievable yield strength is also lower than 550MPa.

Another patent that is closer to the patent of the present invention is the U.S. patent published in 2000, patent number US6056833, "Thermomechanically Controlled Processed High Strength Strong Strong Weathering Steel With Low Yield / TENSILE RATIO; HOT ROLLED, AIR COOLED; PEARLITE-FREE" (see table "Comparative patent 3" in 1) is also a high-strength weathering steel produced by two-stage hot rolling and controlled cooling method, with a yield strength of 70-75ksi (about 483-518MPa) and a low yield ratio of less than 0.85. The patent adopts Cu-Cr-Ni weather resistance composition design and Nb-Ti-Mo micro-alloy design, and the invention patent specially adds V element 0.06-0.14%. Adding V element not only greatly increases the manufacturing cost, but also is not conducive to Regarding the welding performance and low-temperature impact performance of the steel plate, the yield strength of the comparison steel is only guaranteed to reach 483-518Mpa, and no guarantee is provided for the low-temperature impact performance.

Invention content:

The object of the present invention is to provide a high-strength atmospheric corrosion-resistant steel with a yield strength of 550 MPa and a production method thereof. It solves the technical problems that the yield strength of the existing atmospheric corrosion-resistant steel does not reach the level of 550MPa and the low-temperature impact toughness is not good. The composition of the invention is composed of Cu-Cr-Ni and Nb, Ti, Mo and other micro-alloy strengthening elements, and is produced by controlled rolling and controlled cooling, without heat treatment, short production period, simple production method, and low steel cost. In addition to high strength and high atmospheric corrosion resistance, this steel also has excellent low temperature impact performance and good welding, cold bending and other processing properties. Its application fields include railways, road vehicle structures, containers, bridges, building structures, tower masts Columns and more.

In order to achieve the above purpose, the present invention designs a high-strength low-alloy atmospheric corrosion-resistant steel, which is characterized in that the chemical composition (weight%) is: C: 0.05-0.10, Si≤0.75, Mn: 1.0-1.6, P≤0.020 , S≤0.010, Al: 0.01-0.05, Cu: 0.20-0.55, Cr: 0.20-0.45, Ni: 0.12-0.40, Ca: 0.001-0.006, N: 0.001-0.006, in addition to Nb≤0.07, Ti≤ 0.025, two or more of Mo≤0.35, the balance is Fe and unavoidable impurity elements.

The reasons for the limitation of the chemical composition of the 550MPa level high-strength atmospheric corrosion-resistant steel described in the present invention are as follows:

C exists in the form of carbides in steel, and combines with alloying elements to play the role of precipitation strengthening and grain refinement, so the addition amount should not be less than 0.05%, and too high C content is not conducive to welding, so the limit C content should not be high at 0.10%;

Si is an element added to deoxidize the steel. If the Si content is too high, the weldability and the toughness of the welding heat-affected zone will deteriorate, so the upper limit is set at 0.75%;

Mn is an important strengthening and toughening element, which plays a role of solid solution strengthening and improves the strength and toughness of steel. However, too much Mn content increases hardenability, which leads to deterioration of weldability and toughness of welding heat-affected zone. Therefore, it is stipulated that Mn content shall not exceed 1.6%;

S and P have a great influence on the toughness of the steel plate, so the content of S and P should be strictly controlled. As an easy-weldable atmospheric corrosion-resistant steel, the steel of the present invention must be designed with low P composition; high S content not only reduces the low-temperature toughness of the steel , and promote the anisotropy of the steel plate, and the sulfide inclusions will significantly reduce the weather resistance of the steel. Therefore, the steel grade design of the present invention adopts extremely low S and P contents.

Al is an element added to steel for deoxidation. Adding an appropriate amount of Al is beneficial to refine grains and improve the strength and toughness of steel;

Cr is not only an element that improves the hardenability of steel, but also when the Cr content is above 0.20%, it can effectively improve the atmospheric corrosion resistance of the steel. If the content is too high, the welding performance will be seriously deteriorated, so the Cr content should be limited to 0.20%. -0.45%.

Ni can improve the hardenability and significantly improve the low-temperature toughness of steel. It is a favorable element to improve the weather resistance and toughness of steel, and will not adversely affect the weldability of steel and the toughness of the welding heat-affected zone. Ni can also effectively prevent the network cracking caused by the hot embrittlement of Cu. The content is limited to 0.12%-0.40%. If the content is less than 0.12%, the above-mentioned effect is very small, and if it is higher than 0.40%, the cost of steel will be increased, and it is easy to cause the iron oxide scale of the steel plate to be difficult to fall off.

Cu has roughly the same effect as Ni, and mainly acts as solid solution and precipitation strengthening in steel. The proper ratio of Cu-Cr-Ni is the most critical element to improve the atmospheric corrosion resistance of steel, but if the content is higher than 0.55%, it will not only damage the toughness of the welding heat-affected zone, but also tend to cause network cracks during hot rolling, giving Production brings difficulties, so the Cu content is limited to 0.20%-0.55%.

The form of sulfide can be controlled by Ca treatment, and the low-temperature toughness can be improved. When the content is less than 0.001, it has no effect, but if it exceeds 0.006, many CaO and CaS will be produced, and large inclusions will be formed, which will damage the toughness of the steel and even affect the steel. welding performance. Therefore, it is stipulated that the Ca content range is 0.001%-0.006%

In order to further improve the performance of the steel grade of the present invention, Nb, Ti, Mo and other elements are also selectively added to obtain better effects in terms of improving strength and toughness.

Nb, Ti, and Mo can form fine carbonitrides, which are beneficial to refine the grain structure and exert the effect of precipitation strengthening, but when the Nb content exceeds 0.07%, or the Ti content exceeds 0.025%, or the Mo content exceeds 0.35%, then It has an adverse effect on the toughness of the welded heat-affected zone, so the upper limit of the four elements is limited.

The steel of the present invention adopts Ca treatment in production, and its main function is to spheroidize sulfide inclusions to improve the anisotropy of the steel plate and improve low-temperature impact performance.

The invention also provides a production method of high-performance atmospheric corrosion-resistant steel, which adopts pre-desulfurization of molten iron, compound blowing at the top and bottom of the converter, RH vacuum cycle degassing process, and calcium treatment at the same time to obtain the chemical composition (weight %) of the steel For: C: 0.05-0.10, Si≤0.75, Mn: 1.0～1.6, P≤0.020, S≤0.010, Al: 0.01-0.05, Cu: 0.20-0.55, Cr: 0.20-0.45, Ni: 0.12-0.40, Ca: 0.001-0.006, N: 0.001-0.006. In addition, it also contains one or more of Nb≤0.07, Ti≤0.025, Mo≤0.35, and the balance is Fe and unavoidable impurity elements. After the steel billet is reheated above 1200°C, it adopts two-stage controlled rolling, which is characterized in that: the finish rolling starts above 950°C, the cumulative reduction rate is ≥80%, the finishing rolling temperature is lower than 880°C, and as the finished product As the plate thickness increases, the final rolling temperature should be reduced accordingly, and then cooled to 400°C to 700°C at a cooling rate of 5-15°C/S for coiling, and the coiling temperature should also be appropriately reduced according to the increase in plate thickness, and then air-cooled to room temperature . The steel type of the invention does not require post-rolling heat treatment, thereby shortening the production cycle and reducing the production cost.

The invention has the following advantages: on the basis of the low C-Mn steel composition, the patent of the invention adds microalloying elements such as weather-resistant elements Cu-Cr-Ni and strengthening elements Nb-Ti-Mo, and adopts low-temperature final rolling and rapid cooling Production process, so that the microstructure of the steel plate presents ultra-fine grain ferrite and a small amount of bainite, and the yield strength index reaches more than 550MPa, with the following characteristics:

1. The steel of the present invention has excellent comprehensive mechanical properties, the yield strength is 550MPa, which is greatly improved compared with ordinary weathering steel, and the load-bearing capacity is increased. It can be used in various ambient temperatures, especially in areas with low temperature in winter.

2. The steel of the present invention has good atmospheric corrosion resistance, and anti-atmospheric corrosion elements such as Cu, Cr, and Ni are added in the steel to ensure that its atmospheric corrosion resistance is not lower than ordinary weathering steel, and the weathering resistance is 2 times that of ordinary steel. -8 times, the longer the steel is used, the more it can play this advantage.

3. The steel of the present invention has good welding performance. Through reasonable composition design and welding material recommendation, the welding efficiency can be effectively improved and good welding joint performance can be obtained.

4. The steel grade of the present invention is produced by controlled rolling and controlled cooling, delivered as rolled, without heat treatment, simple production process, short production cycle, low steel cost, and can be implemented in various metallurgical enterprises.

Detailed ways:

According to the chemical composition requirements of the steel of the present invention, the converter is used for smelting, and then the post-furnace refining is carried out to obtain the chemical composition shown in Table 1. The continuous casting billet is sent to the hot rolling production line. The billet heating temperature is 1220 ° C. Two-stage controlled rolling and water cooling after rolling are adopted And coiling, the final rolling temperature is 820°C-880°C, and the coiling temperature is 550°C-650°C. The mechanical properties of the inventive steel examples are shown in Table 1. The chemical composition, mechanical properties, etc. were compared with similar steel types. Among them, the comparative patent 1 is CN1609257A "acicular structure high-strength weathering steel and its production method" published on April 27, 2005, and the comparative patent 2 is 1983 3 JP 58045317A "A production method of weldable weathering steel with a strength not less than 50Kg/mm2" published on May 16. Comparative patent 3 is US patent US6056833, which is a high-strength weathering steel produced by two-stage hot rolling and controlled cooling.

Table 1 Steel of the present invention and comparison of chemical composition and mechanical properties of steel grades

The chemical composition of the steel grade of the present invention is obviously different from that of comparative patent 1. The C content of the steel grade of the present invention is 0.05-0.10%, while that of comparative steel 1 is 0.01-0.04%. The chemical composition is also different. The steel of the present invention does not add V, while the comparative patent 2 requires the V content to be 0.01-0.15%, and the comparative patent 3 requires the V content to be 0.06-0.14%.

The mechanical performance requirements of the steel of the present invention are different from those of the comparative steel. The yield strength of the steel of the present invention can meet the performance index of not less than 550MPa, while the yield strength requirements of the three comparative patent steels are all lower than 550MPa, and the performance index of low temperature impact is also lower than 550MPa. Lower than the steel grade of the present invention, the steel grade of the present invention has the requirement of low-temperature impact performance at -40°C, while Comparative Patent 2 does not require low-temperature impact performance. Therefore, the steel grade of the present invention is significantly better than the comparative steel grade in indicators such as strength and toughness.

Embodiment 1-4: According to the composition requirements of the steel of the present invention, the steel of the present invention was smelted on a 300-ton oxygen top-bottom double-blown converter. After RH vacuum degassing treatment, calcium treatment technology was adopted, and the whole process of protective continuous casting; chemical composition The embodiment is shown in Table 2; the billet reheating temperature is 1235°C, the rough rolling start temperature is 1195°C, the finish rolling start temperature is 950°C, the finish rolling finish temperature is 865°C, 825°C, and then the temperature is 8°C/ Cool to 575°C and 550°C at a cooling rate of S, 11°C/S, and air-cool to room temperature. The rolled thicknesses of the first three embodiments are 4mm, 8mm, and 16mm respectively. Examples of mechanical properties are shown in Table 3. The corrosion resistance test results are shown in Table 4.

Table 2 steel embodiment of the present invention-chemical composition

serial number C Si mn P S Mo Alt Cu Cr Ni Nb Ti Ca 1 0.05 0.10 1.10 0.010 0.004 0.14 0.030 0.26 0.22 0.20 0.051 0.010 0.004 2 0.07 0.25 1.20 0.012 0.003 0.19 0.038 0.38 0.35 0.28 0.064 0.024 0.005 3 0.08 0.23 1.40 0.013 0.001 0.22 0.040 0.38 0.30 0.20 0.058 0.023 0.003 4 0.07 0.15 1.24 0.009 0.001 0.25 0.028 0.35 0.42 0.38 0.055 0.020 0.004

Table 3 Invention steel embodiment-mechanical properties

It can be seen from Table 3 that the steel of the present invention has excellent yield strength performance, and the yield strength is all above 550 MPa, which is better than that of the comparison steel. Moreover, this steel type has excellent low-temperature toughness, and the impact energy of AKv at -40°C (full sample) is above 200J. The steel 3 of the present invention was tested for corrosion resistance by using the immersion corrosion test method (TB/T 2375-1993), and compared with the common structural steel Q345C at the same time, the comparison results are shown in Table 4. The test results show that the steel grade of the invention has obvious corrosion resistance while greatly improving the strength, and the corrosion resistance is about twice that of ordinary structural steel.

Table 4 Invention Steel Examples - Corrosion Resistance

The steel of the invention can be widely used in the application fields of railway vehicles, road vehicles, containers, bridges, building structures, towers, columns, engineering machinery and the like.

Claims (1)

1. air corrosion resisting high strength low alloy metal, it is characterized in that the Chemical Composition weight percent is: C:0.05-0.10%, Si≤0.75%, Mn:1.0～1.6%, P≤0.020%, S≤0.010%, Al:0.01-0.05%, Cu:0.20-0.55%, Cr:0.20-0.45%, Ni:0.12-0.40%, Ca:0.001-0.006%, N:0.001-0.006% contains in Nb≤0.07%, Ti≤0.025%, Mo≤0.35% two or more in addition, and surplus is Fe and unavoidable impurities element; Smelting technology is for adopting molten iron pre-desulfurization, converter top bottom blowing, RH vacuum circulation degassing technology by proportioning, carrying out calcium simultaneously handles, steel billet adopts the controlled rolling of two stages behind reheat more than 1200 ℃, the roughing start rolling temperature is 1195 ℃, the finish rolling start rolling temperature is 950 ℃, accumulative total draft 〉=80%, the finish rolling finishing temperature is lower than 880 ℃, is cooled to 400 ℃ to 700 ℃ with the rate of cooling of 5-15 ℃/S and batches, air cooling does not need to roll postheat treatment to room temperature again.